netdev - Re: [PATCH v3 1/9] ptp: Add generic ptp v2 header parsing function

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Date:   Tue, 4 Aug 2020 22:44:48 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Grygorii Strashko <grygorii.strashko@...com>
Cc:     Kurt Kanzenbach <kurt@...utronix.de>,
        Petr Machata <petrm@...lanox.com>,
        Richard Cochran <richardcochran@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jiri Pirko <jiri@...lanox.com>,
        Ido Schimmel <idosch@...lanox.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>,
        Samuel Zou <zou_wei@...wei.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v3 1/9] ptp: Add generic ptp v2 header parsing function

On Wed, Aug 05, 2020 at 12:34:47AM +0300, Grygorii Strashko wrote:
> On 05/08/2020 00:07, Russell King - ARM Linux admin wrote:
> > On Tue, Aug 04, 2020 at 11:56:12PM +0300, Grygorii Strashko wrote:
> > > 
> > > 
> > > On 31/07/2020 13:06, Kurt Kanzenbach wrote:
> > > > On Thu Jul 30 2020, Petr Machata wrote:
> > > > > Kurt Kanzenbach <kurt@...utronix.de> writes:
> > > > > 
> > > > > > @@ -107,6 +107,37 @@ unsigned int ptp_classify_raw(const struct sk_buff *skb)
> > > > > >    }
> > > > > >    EXPORT_SYMBOL_GPL(ptp_classify_raw);
> > > > > > +struct ptp_header *ptp_parse_header(struct sk_buff *skb, unsigned int type)
> > > > > > +{
> > > > > > +	u8 *data = skb_mac_header(skb);
> > > > > > +	u8 *ptr = data;
> > > > > 
> > > > > One of the "data" and "ptr" variables is superfluous.
> > > > 
> > > > Yeah. Can be shortened to u8 *ptr = skb_mac_header(skb);
> > > 
> > > Actually usage of skb_mac_header(skb) breaks CPTS RX time-stamping on
> > > am571x platform PATCH 6.
> > > 
> > > The CPSW RX timestamp requested after full packet put in SKB, but
> > > before calling eth_type_trans().
> > > 
> > > So, skb->data pints on Eth header, but skb_mac_header() return garbage.
> > > 
> > > Below diff fixes it for me.
> > 
> > However, that's likely to break everyone else.
> > 
> > For example, anyone calling this from the mii_timestamper rxtstamp()
> > method, the skb will have been classified with the MAC header pushed
> > and restored, so skb->data points at the network header.
> > 
> > Your change means that ptp_parse_header() expects the MAC header to
> > also be pushed.
> > 
> > Is it possible to adjust CPTS?
> > 
> > Looking at:
> > drivers/net/ethernet/ti/cpsw.c... yes.
> > drivers/net/ethernet/ti/cpsw_new.c... yes.
> > drivers/net/ethernet/ti/netcp_core.c... unclear.
> > 
> > If not, maybe cpts should remain unconverted - I don't see any reason
> > to provide a generic function for one user.
> > 
> 
> Could it be an option to pass "u8 *ptr" instead of "const struct sk_buff *skb" as
> input parameter to ptp_parse_header()?

It needs to read from the buffer, and in order to do that, it needs to
validate that the buffer contains sufficient data.  So, at minimum it
needs to be a pointer and size of valid data.

I was thinking about suggesting that as a core function, with a wrapper
for the existing interface.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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